Monster Media 1996 #15

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≡≡ Introduction Introduction LASICKT SPICE Compiler Utility ------------------------------ LASICKT.EXE (LASI circuit) is a LASI CAD System utility program that can analyze drawings made using LASI and write a SPICE circuit file. It can do both "schematic capture" and "layout capture". LASICKT allows you to first draw a schematic (using LASI) and then simulate the circuit using SPICE. After having done the layout, you can then go back and let LASICKT produce a SPICE circuit file again from the layout, including any parasitic effects that may have been introduced. This version of LASICKT.EXE is a new 32-bit version that will work with drawings made using LASI 5.1. It will use extended memory for large numbers of objects in a drawing. It may also run slower than previous versions because it may have to check a drawing at a finer resolution. SPICE code will be written for circuits with individual devices, and any subcircuit definitions that may be necessary will also be created. In addition to writing a SPICE circuit file, LASICKT also writes a network file that lists the nodes and their device connections. This can be used to check for missing or open connections between a schematic and a layout. Circuit nodes can be marked explicitly, or LASICKT can automatically find nodes on a layout or schematic. The program also can look for certain types of shorts and open connections, and in a rudimentary way calculate the capacitance of interconnections. LASICKT uses normal LASI text objects to mark nodes and to pass device name and parameter information to the SPICE code. Both header and footer text files may be appended automatically to the generated SPICE circuit file. These files may contain extra information such as model and subcircuit definitions or operating statements. LASICKT has a very good use: it can be used to verify that an IC will probably work after the layout has been completely drawn. LASICKT therefore allows "heuristic processing" for students using LASI as an educational tool. The SPICE code produced by LASICKT is written for use with PSpice. If incompatible with another SPICE that you may be using, or if you have a particular problem with the way that LASICKT works, contact the author for possible fixes, advice or improvements. Since doing what LASICKT does is no trivial task, expect future changes. How LASICKT Works The Basic Idea LASICKT works by placing text on specific layers at specific locations in a LASI drawing. In a LASI drawing of an IC or electrical circuit, the circuit devices are simply cells interconnected with lines or areas. To mark how a circuit is connected you use text on two different layers. The two types of text are called NODE NAMES and CONNECTORS. Node Names give the lines and areas used for interconnection in a circuit a definite name. Without a node name, LASICKT will make up a "virtual" name. Connectors locate the "connection points" on a cell and pass that location to higher ranking cells where that particular cell is being connected as part of a larger circuit. This may be diagrammed as follows: ≡≡14 CONNECTOR to | next cell up NODE (Named or Virtual) | / / (marks interconnection with name) | / / ┌──|─/─────────────/──────┐ │ ■C2 ■N1 │ Higher Rank Cell Interconnect Area └────────────────────────┘ Position | CONNECTOR Text (marks connection) Passed Up | / ┌────────|─/─────────┐ │ ■C1 │ Lower Rank Cell Interconnect Area └────────────────────┘ In the above, connector C1 is connected to node N1 in the higher cell. This process of passing connections can be extended to the full depth of cell nesting. Cell nesting in LASI is similar to the way that SPICE works, that is, SPICE arranges devices into subcircuits which correspond to LASI's cells. LASICKT's NODES (named or virtual) correspond to what SPICE calls nodes, however CONNECTORS are graphical entities that have no real equivalent in SPICE. SPICE code also requires that you give devices NAMES and pass certain device PARAMETERS. To indicate device names and parameters you use two additional layers and write the text directly on the cells. The text is literally passed on to the SPICE code. LASICKT uses text written on a total of four different layers to control the SPICE code that it generates. Device Definition Statements A device statement in SPICE can be considered to have three fields. LASICKT builds a device definition by filling in these fields using text that it finds on a drawing: ≡≡4 ┌──────┬───────┬───────┐ │ NAME │ NODES │ PARAM │ └──────┴───────┴───────┘ NAME is the a predefined device name beginning with R,C,Q, etc. It may also be a subcircuit name starting with X. NAME may also include a logic device type (NAND(2) for example). When you use LASICKT this text is placed on the "Device Name Text Layer" and is passed to the definition as the first field. NODES is a sequence of node names that LASICKT constructs, and is placed second in the SPICE definition. The node names are determined from node name text and any virtual node names. PARAM is text placed on a "Parameter Text Layer". It is passed literally to the last field. This contains such things as MODEL and SUBCKT names and adjustable parameters. This text can become pretty wordy so multiple lines are allowed. Devices, Subcircuits and Cells It is important to understand how SPICE devices translate from LASI cells. LASI's boxes and paths are NOT devices; they only serve to connect things together (on interconnect layers). A minimum device is a rank 1 cell. For example, a single NPN transistor, whether drawn as a symbol or a layout figure is a simple device (Q-type). A NAND gate even though it may have several transistors and resistors is a single U-type device. If several devices are connected together they form a subcircuit (SUBCKT), which can be used as an X-type device. A LASI cell must be at least rank 2 to become a subcircuit since it must contain other cells. To add to the confusion, there is no reason why you can't define a SUBCKT separately, and include it as a rank 1 cell in a cell of rank 2 or greater. You can conclude however that rank 1 cells will contain no nodes or node name text, since they have no devices to interconnect. (There is an exception with global symbols explained below.) Rank 1 cells will however have connector text to tell any higher cells where to connect to them. A rank 2 cell will normally have nodes that connect its devices or cells together. If a rank 2 or greater cell is the "top" cell it will have no connectors; otherwise it will have connectors to connect itself to the cell above it. A top cell will always have node names on its external connections so that it can be properly referenced for input and output. Types of Text Node Name Text Node name text is LASI text that labels an object (box, path, polygon or line) that is used for interconnection with a definite name. Applying certain rules, LASICKT finds just which objects on a certain layer are connected geometrically together into what might be called a "node island", and gives them the node name that labels (at least) one of them. These node names are placed directly in the SPICE code. Named nodes are only "seen" by LASICKT within the cell that contains those objects. Virtual Nodes If it finds connections without a node name, LASICKT is smart enough to make up its own name for a node. Once LASICKT has looked for all possible associations between node name text and lines and areas, it will make up a "virtual" node name for any lines or areas that remain. This is not actual drawing text, but a number with a prefix you can choose. As with node name text, these node names will be placed in the SPICE code. Note: Once one or more objects are found by LASICKT to be a single node island and they have been given a node name (text or virtual), those objects collectively can be called a "node", which is what SPICE actually refers to as a node. Connector Text Connectors MUST be placed on a layer different from node name text. Connector text "communicates" the nodes of a cell up to a higher rank cell that contains that cell. In the higher cell, the connector is "attached" to an object that is used for interconnection. Connectors are only "seen" by LASICKT in the higher ranking cell. Connectors locate the "electrical connection points" in a cell, and are normally placed on a cell in locations that "electrically connect" to the outside world. Connector text MUST contain a SEQUENCE NUMBER in the text that indicates the RELATIVE ORDER of the nodes in the SPICE device definition statement. For example, an NPN transistor might have the connectors "1-C", "2-B", and "3-E" that correspond to the SPICE transistor device's node order. The number of the connector will be taken from the first digit found in the text, that is, "1-C" and "C-1" are equivalent. At the moment, 64 connectors are permitted on a single cell, and a total of 2048 connectors may be passed to the next higher cell. Note: Different cells can use the same connector text and sequence numbers, since only the relative order of the sequence numbers in a particular cell is important. Name and Parameter Text SPICE requires devices to be named, and also needs various parameters to be included in device definition statements. LASI text may be used to pass literal text information to SPICE definitions. Two different layers are used to pass DEVICE NAMES and DEVICE PARAMETERS independently. You simply write this information on your drawing and it is passed to SPICE. Since a cell is a device, to pass text to SPICE, you place the text reference point within the OUTLINE of the cell. This associates the text with that cell only. Be careful not to put text on more than one cell or it will be passed to all. If you put device text IN a cell but not ON any lesser cells, the text is used to construct a SUBCKT if the cell is not the top cell. A drawing that is to be processed by LASICKT is therefore a well documented drawing, since each cell will have information about itself written directly on it. Global Symbol Cells As a compromise with standard practice used in schematics, LASICKT allows you to make rank 1 cells into little objects that act like box objects that may be used to interconnect devices. The difference is that they carry around a node name and a little picture. The best example is a ground symbol. To SPICE this is a global node "0", but when you use it in a drawing it connects to only one point. It therefore labels a node as grounded, but connects nowhere else. To make a global symbol you take a rank 1 cell and place NODE NAME text on it. You place NO CONNECTOR text on it as you would do normally to connect to the cell. The OUTLINE of the cell becomes equivalent to a box of the same dimensions, and if a connector from another cell falls in that area, the cell's connector is labeled with that symbol's node name. For example, if a ground symbol cell overlays a connector on a transistor's emitter, and if that symbol cell has "0" on the node name layer written on it, that emitter is then set at node "0", and forever grounded. Note: Any global node names other than "0" should be declared in a .GLOBAL statement in the SPICE file. Text Placement Rules Node Name Text Rules For named node text to label drawing objects, the text must be located so that the text can be uniquely identified. The following rules apply to the placement of node name text: 1. Text is always located by its reference point and is independent of the size of the text or its orientation. 2. Node name text must be located on objects that are on one of the layers used for interconnection as follows: For boxes, the text reference must be ON an edge or WITHIN the area of the box. For paths WITH WIDTH, the text reference must be WITHIN the path area or ON a horizontal or vertical edge. For OPEN paths WITHOUT WIDTH (lines), the text reference must be ON a vertex or WITHIN a horizontal or vertical segment. For closed paths WITHOUT WIDTH (polygons), the reference must be WITHIN the area of the polygon. Connector Text Rules Connector text can be located anywhere, but should be located where actual electrical connection is to be made in a layout or schematic. There is NO checking that an actual electrical connection is made or that any design rules ar obeyed. Connector text follows these rules: 1. Connector text MUST ALWAYS be connected (or attached) to an object used for interconnection in the NEXT HIGHER CELL. If not, you will get an "Open" error when you run the program. 2. A connector is attached to a node in the NEXT HIGHER CELL following the same rules as node name text listed above. 3. If you place a NODE NAME text reference point EXACTLY on the CONNECTOR text reference of the cell below it, the connector will connect to the node. This has a very handy if you want to connect to a point that is not on an interconnect layer. An example would be connecting the substrate of a transistor which normally has no metallized connection. Passed Text Rules For text to be passed to the SPICE code, certain rules must be followed: 1. Device name and parameter text must be located on two different layers that are different from the node or connector text layers. 2. The text reference must be located WITHIN or ON the OUTLINE of a lesser cell to be passed that SPICE device. 3. If a PARAMETER text reference is NOT on the OUTLINE of ANY cell, it will be passed to the SUBCKT definition if the overall cell is made into a SUBCKT. 4. LASI text is up to 40 characters long. If more is needed multiple lines must be used. 5. Text on multiple lines will be assembled into a single line in a descending Y order. 6. If a "+" is placed at the beginning of a text string a new line (CR-LF) will be inserted, which corresponds to SPICE convention. 7. If a "*" is placed at the beginning of a text string a new line will be inserted. This lets you put comments in the SPICE code. 8. Each text line will have a SPACE inserted after it, so that on multiple lines you don't have to put spaces in your text. Interconnection Rules Interconnection Rules LASICKT connects objects (boxes, paths, polygons and lines) following these rules: 1. Objects must be in the same cell and be on the same layer or layer group to connect. 2. Several interconnect layers may be listed in the program setup. If they are listed separated by spaces they are all independent and do not connect to each other. 3. If layers are listed separated by spaces but in a GROUP enclosed in PARENTHESES, they all interconnect as if they were a single layer. 4. Boxes, paths with width and closed polygons are all AREAS. 5. Areas connect if they overlap or are contiguous on a horizontal or vertical edge. 6. Open paths without width are LINES. 7. Lines connect if they have ANY vertices that are coincident. 8. Lines connect if a vertex of one falls WITHIN a horizontal or vertical segment of the other, as in a "T" or an "L". This is normal schematic convention. If an interconnection has to go through some kind of a crossover structure on a different layer (a polysilicon underpass for example in an IC), you must do one of the following: ■ Place the same node name on the interconnect objects on both sides of the crossover to indicate that it is the same electrical node. If the crossover object is also used for connection, put the same node name text on that object or on the overlap, and list that object's layer as an interconnect layer. Do not list the different layers in a group in parentheses, or they will short out if one layer crosses another. ■ Make the crossover into a cell and give the end nodes different node name text, or leave off the node name and allow them to be virtual nodes. The latter is useful if the crossover has some electrical effect, such as significant resistance. Also note that you can't put the crossover and the interconnect layer in a group enclosed by parentheses, because they will short out. LASICKT does not know how to trace through different layers in an IC to determine connections since it is not "process specific". Capacitance Capacitance LASICKT will calculate the approximate parasitic capacitance of the interconnect layers to ground, and add a capacitor device to the SPICE code. For the moment this is the same for all layers, but may be made layer dependent in the future if it really proves valuable. LASICKT calculates all the areas, but ignores overlaps. Lines used in schematics are ignored. The capacitance is in pF per square physical unit that you used to do your drawing, i.e. pF/sq-um typically. The parasitic capacitor will be named "C_NODE", where NODE is the node name text that labels the areas. Running LASICKT LASICKT Setup When you first run LASICKT from the DOS command line, it will come up in a setup screen. The setup is saved as LASICKT.SET and returned when you run the program again. The setup parameters are as follows: ■ Name of the Cell. This is the main cell that you want analyzed and converted. The program will produce a SPICE file with the extension ".CIR" using this cell name. The net list file will be written with the cell name but with a ".NET" extension. ■ Header and Footer Files. These are the names of files you may want to include in the SPICE file. These filenames may be "global" files used with several drawings and therefore may include a path. These files may contain such things as .MODEL definitions of your devices. These are completely arbitrary and may be omitted by simply putting in a name of a file that doesn't exist or leaving the name blank by entering only a space character. ■ Interconnect Layers. These are the layers that are used for connecting devices, if more than one. These numbers should be separated by a space and groups may be enclosed by parentheses to allow more than one layer to connect. For example,"2 (4 8)" will connect 2 independently, but 4 and 8 will connect together. You may enter a maximum of 8 layers or 8 groups of up to 8 layers. ■ Interconnect Capacitance. This is the approximate unit capacitance of the interconnect layers to ground. The capacitance is in pF per square physical unit that you used in your drawing, i.e. pF/sq-um typically. If you make this parameter equal to zero (0). the program will run faster because it will not bother to calculate the areas of the various interconnections. ■ Named Node, Connector, Device Name and Parameter Text Layers. These are the layers that you used for those respective text in your drawing. All must be different layers, and all must be layer 1-64. ■ Error Switches. These are used to control error checking and reporting. These are explained separately below. ■ Virtual Node Prefix. This is the name of any virtual nodes to which a number will be added. This should be short as possible, and case is preserved. ■ Error Destination. This allows you to print or save any errors that are found. The parameter must be one of the printers "LPT1", "LPT2", "LPT3" or "PRN" (=LPT1), "FILE" for the file LASICKT.ERR or leave it blank for no report. With no report option, the program pauses so that you can read the error. To run LASICKT after the setup, press ALT-G or click "Go". To abort at any time, press ESC. Error Switches The final setup line contains four yes/no switches. These control the following error checks: Opens If LASICKT finds that a connector on a cell is "open" it will warn you. To be connected, the connector must be attached to an interconnect layer in the higher ranking cell where the cell is used. Attaching a global symbol or putting a node exactly on the connector will also satisfy the connection. This is an error that is easy to make. An "open" connector will be written to the SPICE code as a "?", since there will be no node name available. When you are satisfied that there are no actual errors, you can set this to "N". Shorts If LASICKT finds two objects connected but with different node names, it will report it as a "short". SPICE code will still be written, but it could have a node conflict that your SPICE analysis program should eventually discover. You might see the same error twice. LASICKT cross checks, so that if one object connects to a second, the second will also be found to connect to the first. A second way you can have a short is if you put more than one connector with the same sequence number on a cell. This is permitted, but it possible to connect different nodes to the same actual connector. The error message will indicate the cell and the position. If you are sure that there are no shorts, set this to "N" and the program will run faster because the number of objects checked will be greatly reduced. IMPORTANT: Shorts checking on interconnections should not be confused with checking for shorts on an overall layout. LASICKT checks for node naming conflicts, not actual shorts, since it really doesn't know how a circuit is to be connected. It checks only at a single cell level, and not the composite of several cell nestings. Floats This indicates that a cell exists that is not attached to anything in the circuit. This will detect cells that you forgot to connect, or such things as test transistors that would not be normally connected. Turn off the warning message with "N" if you have a problem. Failure of this test is just a warning since the floating device will not appear in the SPICE code. Devices This checks if a device definition statement contains both device name and device parameter text. All SPICE devices require that you specify the device name and almost all devices have parameters of some kind. This does not check the correctness of the text, just if it is present. A SPICE statement will contain "???" if device text is missing. Turn this test off with "N" if it causes any problems. Failure of this test usually incorrect device statements. Run Operations As LASICKT analyzes a drawing it will indicate what it is doing in the "Operations" box. It will show the name of the cell and the particular operation. Any error warning messages will appear in the "Messages" box. A count of the devices, nodes and connectors will be displayed in the "Counts" box. This is useful to see just what LASICKT has found, and to verify just what you think it should find. This is explained below. LASICKT will first search for global symbols in the drawing cell collection. Then, for the main circuit and each possible subcircuit, it will search for the nodes that you have named, and then it will try to connect the objects on the interconnect layers. It will then try to create and connect any virtual nodes that may be needed. Connecting virtual nodes takes somewhat longer. Whenever LASICKT looks for interconnections it does multiple passes, extending connections one at a time, until it finds no more. Hint: To speed things up, use named nodes, not virtual nodes, unless you have a fast computer or can wait. Every time a virtual node is created there has to be a complete search of all interconnections. Finally, once it has learned enough about your drawing, the program will write SPICE code to the .CIR output file, and will write network list information to the .NET file. This will be done in stages, depending on any subcircuits. Each cell listed as being analyzed will be translated into either the main circuit or into a subcircuit definition. Count Listing While LASICKT is running it gives a count of several things: ■ Devices is the number of SPICE devices found in the cell being analyzed. It is actually the number of cells in the cell. These would correspond to basic devices (transistors, resistors, etc.) and subcircuits (X-type devices). ■ Nodes are listed by (Nam)ed, (Vir)tual and (Total). The named nodes are found first and then the virtual nodes are generated. The total will be the actual number of different nodes that will be identified in the main circuit or subcircuit. ■ Connectors are listed by (Cnt) or Count, which is the number of Connector Text instances that have been found on the cells below the cell being analyzed. This number is broken down into what kind of nodes they connect to in the analyzed cell. (Nam) is the number assigned to named nodes, (Vir) is the number assigned to virtual nodes and (Sym) is the number of connectors assigned to global symbols. The (Total) is then the sum of all the named, virtual and symbol nodes connected to the connectors. This should be equal to the initial Count. Using Net Lists The Net List File When LASICKT finishes writing SPICE code statements for a circuit, it resorts the information and uses it to write a list of nodes and their connections in the Net List File. The name of this file is the main cell name with the extension ".NET". Each node name is followed by the device names and the connector sequence number for each device connection. The name and number are separated by a period. "R2.1" for example says that connector 1 of device R2 is connected to a particular node. The main circuit and any subcircuits are listed independently. Remember that node names are local and belong only to the circuit in which they appear, (except for global nodes) and should not be confused with similar node names in different circuits. Net List Compare If you want to compare two network lists, a program NETCOMP.EXE is supplied. This program looks at two list files (schematic and layout) and indicates errors where node connections in the first file are missing on the same node in the second file. This should indicate a wrong connection in the layout, assuming that the schematic is correct. NETCOMP then interchanges the list files and checks in reverse (layout to schematic), finding any connections in the first file that are not in the second. The names of nodes and connectors are case independent. It is however necessary that schematic and layout nodes, connectors, and devices be named exactly the same, or an error will be reported. If you let LASICKT add its own virtual nodes, there is no guarantee that nodes will be named the same in schematic and layout. To avoid this problem, you need to put Node Name Text on all your nodes. NETCOMP is a new program, so any comments will be appreciated as to the best strategy that should be used to do net list comparisons. An Example An Example The best way to see how LASICKT works is to have an example. The LASI tutorial layout (compressed in TUTOR.ZIP) contains a layout of a small opamp (OPAMP) and a schematic ($OPAMP). This has been marked with text so that LASICKT can process it. The node names are on layer 60, connectors 61, device names 62 and parameters are on layer 63. Interconnections are metal on layer 8 for the layout and 32 for the schematic. There is also a global cell used for the ground symbol. The PNP current source is a separately defined SUBCKT that can be found in OPHDR.LIB. Notice that only a few nodes are marked. The rest are virtual nodes. This is probably what would normally be done by someone using LASICKT. You only need to use text if you want to force a name. (such as "0") You can run LASICKT on OPAMP or $OPAMP and see what is produced. You will find a few intentional errors - try to fix them. If you do run LASICKT on OPAMP and $OPAMP, the net list produced will not agree. Trying to make the lists agree when read by NETCOMP is left as a learning exercise. Using a Flat Drawing Using a Flat Drawing LASICKT can be used to check for wrong connections in layouts more effectively if the layout is "flat", that is, all the interconnecting layers are in a single main cell. The basic nature if SPICE hierarchy generally precludes this because devices are usually nested in SUBCKT modules, or in a layout as LASI cells. A program FLATTLC has been added to LASI 5.1 which will take a main cell and its lesser cells in TLC format and convert to a single large flat TLC file. When converted back to internal form, this new flat cell can be used by LASICKT to do more complete checking. The disadvantages of using a flat cell are first, the complete cell may have too many objects and exceed the limits that LASI can use as an internal cell, and second, running LASICKT on a large number of objects can take a long time, unless you have a very fast PC. When LASICKT compiles a SPICE circuit file, it must find devices or SUBCKTs represented as cells in the drawing. All LASICKT really needs is the LOWEST level of nested cells and any connector and device (name and parameter) text located on the cells. To better understands this, consider if LASICKT finds a cell in the drawing that has other cells nested in it. LASICKT will define this cell as a SUBCKT with the lesser cells represented as device or subcircuit statements within it. If you were to expand every SUBCKT, eventually, all subcircuits would break down to the lowest device definitions, unless they are externally defined in a LIB file. (PSRC1 in the tutorial opamp is one of these.) FLATTLC replaces SUBCKT definitions with their components until only cells representing devices remain. It then breaks down these cells into their basic objects (boxes, paths and text) and makes a token device cell containing any connector text. It also adds a box object that is the same size as the outline (from the TLC header) of the original cell. This keeps the cell outline the same so that device name and parameter text can be found by LASICKT correctly. FLATTLC also removes any device name and parameter text that is NOT one nested level up and is NOT located within the outline of a token device cell. This eliminates possible conflicts from device name and parameters on subcircuits which contain the lowest devices. FLATTLC will also remove ALL node name text EXCEPT that which is in the main flattened cell. Generally, you may not use the same node names in nested subcircuits. If LASICKT compiles a flat cell, it will signal a short error if all node names are not exactly the same on contiguous interconnects. Notice that after a drawing is flattened, it is really simpler in certain ways: It has only rank 1 token device cells and all interconnections are just basic objects on one or more fixed layers. How devices are connected is immediately obvious (to LASICKT), and connections to devices are made by a single level of connector text in each cell. There will also be only a single level of device name and parameter text located on token device cells. All other connector, device name and parameter text on higher nested cells in the original drawing will have been removed. There are at least two ways you can use a flattened cell to check for design and layout errors: 1. You can run LASICKT on it as is, and let SPICE analyze it for correct functioning. LASICKT will make named nodes from any contiguous named interconnect objects and virtual nodes from contiguous unnamed objects. 2. You can put in NODE NAMES on ALL interconnect areas at the MAIN CELL level in the original unflattened drawing and let LASICKT look for shorts in the flattened drawing. Once flattened, named nodes that wrongly connect become very obvious to LASICKT and are caught as shorts. Parameter Line Editor Parameter Line Editor LASICKT now uses a simple line editor that resembles the editor used with Windows. The editor operates as follows: ■ To move from parameter to parameter, press the UP/DOWN ARROW keys, (SHIFT)TAB, or click the mouse on a parameter. ■ Press PGUP/PGDN to move to the first or last parameter. ■ Press LEFT/RIGHT ARROW to move the text cursor left or right. ■ Press HOME/END to move the cursor to the beginning or end of a line. ■ Press BACKSPACE to erase a character to the left of the cursor. ■ Press DELETE to erase the character to the right of the cursor. ■ Press CTRL-BACKSPACE to completely erase a text line with the cursor at any position. ■ When you first select a parameter, typing any printable character other than SPACE or LEFT/RIGHT ARROW will replace the whole text line. ■ If you make a mistake press ESC to restore the original text.